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The chemistry of small‐ring compounds. Part 47. Small‐ring interference in the ozonolysis of cyclopropylidenecycloalkanes

1984; Royal Netherlands Chemical Society; Volume: 103; Issue: 7-8 Linguagem: Inglês

10.1002/recl.19841030704

1878-7096

C. J. M. van den Heuvel, Amy K. Holland, J. C. van Velzen, H. Steinberg, Th. J. de Boer,

Organic Chemistry Cycloaddition Reactions

Abstract Ozonolysis of olefins Ia‐c containing a cyclopropylidene group, does not follow the classical Criegee mechanism but gives the anomalous products IIa‐c, IIIa‐c,IVa‐c and Va‐c , as outlined in Scheme 2. None of these oxidation products contains the cyclopropyl ring any more. It is suggested that primary ozonides containing a cyclopropyl moiety, undergo already at low temperature simultaneous 0–0 homolysis and small‐ring fission, thus generating the key intermediate 1, 6‐biradical X (Scheme 4). This is at the same time a peroxy and a carbon radical, which upon combination – in casu cyclisation – gives the six‐membered peroxa‐ketone II . Apart from combination, biradical X can also undergo intramolecular disproportionation to the unsaturated ketone XIX (Scheme 8) containing a terminal hydroperoxy function. This product does not accumulate as such, but is further oxidised to the epoxide Va‐c with simultaneous formation of the five‐membered cyclic 1, 3‐oxa‐ketone IIIa‐c ( cf Scheme 8). The least oxygen‐rich reaction product is the cyclobutanone IV , for which zwitter ion XIV or its ring‐expanded isomer XV (Scheme 6) is a likely precursor. Interception of the first zwitter ion by methanol, followed by loss of oxygen, explains the formation of glycol derivatives VI (Scheme 6). Direct attack of XVIII (Scheme 8) on starting material, provides an other route towards the cyclobutanone IV , which is suppressed in the presence of diphenyl sulfide and cinnamic ester.